The present invention relates to an embedded permanent magnet type induction motor.
A prior art embedded permanent magnet type induction motor (hereinafter referred to as the induction motor) will be described below with reference to FIGS. 1 and 2. FIG. 1 shows a rotor core plate which constitutes the rotor of the induction motor, and FIG. 2 is a perspective view schematically showing the stator of the induction motor.
Referring to FIG. 1, a rotor core plate 40 is a circular thin plate having an aperture 41 in its center. A plurality of rotor slots 42 in which conductors, respectively, are to be embedded are provided in the rotor core plate 40 on the outer peripheral side thereof in the state of being spaced in the circumferential direction at constant intervals. A plurality of holes 43 in which plate-shaped permanent magnets, respectively, are to be embedded are formed in the area between the aperture 41 and the rotor slots 42. The holes 43 are formed in such a manner that four holes are symmetrically disposed.
After a multiplicity of rotor core plates 40 have been formed into a lamination, conductors (not shown) are embedded into the respective rotor slots 42 by injection molding techniques, and permanent magnets (not shown) are embedded in the respective holes 43.
It is known that motor performance can be improved by giving a skew angle to the extending direction of each coil embedded in the stator or each of the conductors embedded in the rotor.
FIG. 2 shows a stator in which the skew angle is realized. As shown in FIG. 2, a stator 50 is formed of a lamination of a multiplicity of stator core plates 51. Each of the stator core plates 51 is a circular plate having an aperture 52 in its center. A plurality of stator slots 53 in which coils, respectively, are to be embedded are provided in each of the stator core plates 51 on the inner peripheral side thereof in the state of being spaced in the circumferential direction at constant intervals.
After a multiplicity of stator core plates 51 have been formed into a lamination, coils (not shown) are embedded in the respective stator slots 53. Particularly when the stator core plates 51 are being laminated one by one, the stator core plates 51 are laminated while the position of each of the stator core plates 51 is being deviated from that of the previous one in the circumferential direction to a slight extent, whereby a skew angle xcex2 is formed.
As described above, the reason why the skew angle xcex2 is realized in the stator 50 is that the stator core plates 51 needs to be laminated while each of the stator core plates 51 is being deviated from the previous one in the circumferential direction to a slight extent. In other words, in the case of the rotor 40 shown in FIG. 1, because permanent magnets need to be embedded in the respective holes 43, the rotor core plates 40 cannot be laminated while each of the rotor core plates 40 is being deviated from the previous one in the circumferential direction.
However, during the work of embedding coils in the respective stator slots 53 after laminating, workability and productivity are inferior because passages each formed by a multiplicity of stator slots 53 arranged consecutively are extended in the inclined direction.
Therefore, the present invention provides an embedded permanent magnet type induction motor which makes it possible to improve workability and productivity during the manufacture of motor bodies.
An embedded permanent magnet type induction motor according to the present invention comprises a rotor made of a plurality of rotor core plates laminated to an axial length L along its central axis. Each of the plurality of rotor core plates has a plurality of rotor slots in which coils, respectively, are to be embedded. The plurality of rotor slots are spaced apart from one another in a circumferential direction of the rotor. Each of the plurality of rotor core plates further has at least two holes in which permanent magnets are to be embedded.
According to an aspect of the present invention, each of the rotor core plates is provided with the plurality of rotor slots each inclined by an angle xcex1 with respect to a radial direction of each of the rotor core plates. The rotor has the axial length L being made of laminations divided into at least two equal portions with respect to the central axis. The divided laminations are combined with one another so that one of the divided laminations is opposed to another in inclination of the angle xcex1 and the plurality of rotor slots of one of the divided laminations are respectively superposed on the rotor slots of another at at least their ends closer to the central axis of the rotor to form a skew angle xcex2 in each of passages formed by the plurality of rotor slots extending along the axial length L.